1. Field of the Invention
This invention relates to a tire pressure gauge, more particularly to a tire pressure gauge having a replaceable biasing member so as to be suitable for use in measuring of tire pressures of different tires.
2. Description of the Related Art
A conventional tire pressure gauge, such as those disclosed in U.S. Pat. Nos. 2,225,675, 5,886,254 and 6,525,655 B2, uses a flexible diaphragm to raise a piston in response to air pressure introduced into a casing from a detected tire such that the movement of the piston relative to an indicating member secured in the casing, can indicate the tire pressure of the tire. Since quality deviation often occurs in the manufacturing processes, means for correcting the initial position of the piston is needed for maintaining the precision of the tire pressure gauge.
U.S. Pat. No. 5,939,627 granted to the present inventor discloses a tire pressure gauge with an adjustable extension member to adjust the length of an outwardly extending portion of a plunger or to correct the position of the graduations provided on the plunger relative to a pointing end of a tubular housing where a detected pressure is read. However, the adjustable extension member, which is not fastened to the plunger, may rotate with a slender pen element during adjustment of the adjustable extension member, thereby resulting in inconvenience. Moreover, to measure different tire pressures, a spring for biasing the piston towards a pressure inlet hole has to be replaced so as to change the biasing force. However, replacement of the spring is not convenient in this tire pressure gauge.